Functional Characterization of a Novel Variant of the Constitutive Androstane Receptor (CAR, NR1I3)

Viktoria Prantner,Paavo Honkakoski,Yuval Cinnamon,Ferdinand Molnár,Jenni Küblbeck

doi:10.32527/2018/101386

Viktoria Prantner, Paavo Honkakoski + Show 3 more

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https://doi.org/10.32527/2018/101386

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The nuclear receptor constitutive androstane receptor (CAR; NR1I3) controls the inducible expression of many enzymes and transporters involved in drug metabolism and transport, energy metabolism and toxicity. Single nucleotide variants of CAR are quite rare and usually associated with changes in pharmacokinetics of therapeutic drugs. Recently, a non-synonymous variant (F243S in the wild-type CAR) has been linked to the Kleefstra syndrome (MIM 610253) affecting neurological development. We identified another, previously unknown CAR variant (I281T) in a patient suffering from Kleefstra-like symptoms. Detailed reporter gene assays and molecular modelling indicated that the I281T mutation decreases the ability of CAR to recruit co-activators, likely by interfering with the assembly of functional CAR/retinoid X receptor (RXR) heterodimers. Although the I281T variant does not seem to cause the features of the patient, the present study adds to our knowledge about CAR function.

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The constitutive androstane receptor CAR (NR1I3) is a ligand-activated transcription factor that regulates the inducible expression of many enzymes and transporters involved in drug metabolism and transport [1,2,3]
The constructs containing only the CAR ligand-binding domain (LBD) region (Figure 1B) showed a similar 47–72% decrease in GAL4-responsive reporter activity by the I281T mutation. This indicates that the I281T mutation may affect binding of either ligands or proteins interacting with the LBD
The inverse agonist S07662 attenuated LUC activity to similar levels, with a decrease of ∼90% for the wildtype CAR and ∼60% for the I281T mutant. These findings suggest that decreased I281T activity was not caused by insufficient availability of cellular coactivators

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Introduction

The constitutive androstane receptor CAR (NR1I3) is a ligand-activated transcription factor that regulates the inducible expression of many enzymes and transporters involved in drug metabolism and transport [1,2,3]. Nuclear Receptor Research protein phosphatase 2A [11], or by direct ligand binding [1, 12, 13]. Cell-based assays have identified two very rare non-synonymous SNVs in the ligand-binding domain (LBD) that decrease constitutional or ligand-elicited transcriptional activity [3, 20]. These mutations (H246R, L308P in wild-type CAR) are not present in ExAC. More common intronic SNVs (e.g. rs3003596; rs2501873; rs4073054) or synonymous SNVs (e.g. Pro180Pro; rs2307424) are associated with changes in efavirenz pharmacokinetics and side effects [24,25,26], outcome of sunitinib therapy [27] or warfarin dosages [28], presumably via an effect on CAR expression and subsequent changes in levels of enzymes metabolizing these drugs

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